Shaped articles having a simulated stone appearance and methods for producing such articles from filled polymeric resins are known. One principle form of simulated stone is prepared by blending a colorant and resin matrix to yield a random pattern of veining or striations giving an appearance similar to marble or onyx. This type of material is disclosed, for example, in U.S. Pat. Nos. 4,244,943 and 4,849,456.
A second principle form of simulated stone is prepared by blending colored particles in a resin matrix to yield a granular pattern which gives an appearance similar to granite or the like. In the preparation of artificial granite, it is important to employ a filler material having adequate heat stability and particle size. Moreover, it is essential that partial or full dispersion of the filler material and the resin substrate be achieved in order to provide a reproducible effect. Inadequate dispersion of the filler particles often results in particle agglomeration. This yields an unattractive blotchy or dappled appearance due to the streaking or smearing of the particle agglomerations within the resin matrix.
Prior to the present invention, granite-like simulated stone materials were prepared by dispersing filler particles in a substrate thermosetting resin. In the case of thermoset resins, the chemical reaction is only partially complete when the fillers are added, and is concluded when the resin is molded. This results in a non-meltable cross-linked resin article which cannot reworked. The advantage of using thermosetting resins is that the viscosity prior to cure is relatively low which facilitates the solubilization or random dispersion of the filler particles within the resin matrix.
U.S. Pat. No. 4,107,135 describes dappled articles which contain: (A) 20-70 parts by weight of a cross-linked polymer having a glass transition temperature of at least 70.degree. C.; (B) 80-30 parts by weight of an inert filler; and (C) 0.01-2 percent by weight of the article, of short, colored fibers.
U.S. Pat. No. 4,137,215 describes a process for imparting a reproducible decorative effect in a molded plastic article comprising the steps of: (A) forming a molded composition by mixing (i) a curable thermosetting binder material, (ii) at least one inorganic filler, (iii) glass fiber and (iv) solid polymer particles in an amount from 0.1 to 20 percent by weight, based on said binder, said particles being a homopolymer or copolymer of styrene or of polyvinyl acetate; and (B) placing said composition in a mold and subjecting the same to elevated temperatures and pressures sufficient to (A) cure said thermosetting binder material, but (B) insufficient to effect more than partial solubilization of polymer particles in said binder material.
U.S. Pat. No. 4,235,948 describes a method of bonding a composition containing a catalyzed polyester bonding resin and a simulated stone aggregate to a preformed acrylic sheet. The simulated stone matrix composition comprises a catalyzed polyester bonding resin, a simulated stone aggregate, pigmenting agents and a selected exothermic reducing agent.
A disadvantage of the above procedures is their inapplicability to thermoplastic resin substrates. For thermoplastics, the polymerization reaction has been completed. Thus, the materials may be processed at or near their melting point, and scrap may be reground and remolded. This allows processing to be achieved by a wide variety of methods including extrusion, co-extrusion, thermo-forming, blow-molding, injection molding, compression molding, calendaring, laminating, stamping, pultrusion, etc.
There continues to be a need for a reproducible granite-like simulated stone effect in thermoplastics without problems such as heat stability and particle size of the filler, as well as smearing or streaking often caused by poor filler dispersion.